Evaluation of alternative development process for high-aspect-ratio poly(methylmethacrylate) microstructures in deep x-ray lithography

The development of very thick commercial sheets of poly(methyl methacrylate) (PMMA) resist patterned by deep x-ray lithography was investigated. The development characteristics were explored, with the alternative methyl-iso-butyl-ketone (MIBK)-based developer systems, MIBK and MIBK/ iso-propyl-alcohol (IPA) 1:3, being compared with the “GG” developer system (2-butoxyethoxy-ethanol, morpholine, 2-aminoethanol, and water) more generally used. In particular, the influence of various parameters were studied: PMMA characteristics (resist thickness, pre-exposure thermal treatment), exposure conditions (x-ray incident energy, dose at the bottom of the resist, rate of dose deposition, distribution of dose inside the resist), development conditions (temperature, megasonic-assistance, length of cycle into developer and rinse baths), postexposure treatments (storage, thermal treatment), etc. The study also focused on surface finish of the parts corresponding to different exposure and development conditions. Using MIBK/IPA megasonic assisted development and postexposure treatment at 40 °C resulted in the best conditions, faster development rate, as well as smoother developed surfaces.